In most conventional types of heavy-duty excavating machines of the dragline or stripping shovel type, there is usually provided a rotatable frame having a top deck and a bottom plate. A stationary ring gear is mounted to a base of a crawler unit or to a tub which is supported on the ground adjacent to or in a pit of a surface mine. The rotating frame supports at least one drive unit, having a pinion drivingly engageable with the ring gear which operates to swing the rotatable frame. Traditionally, such swing drive units have been mounted on the top deck with the pinion shaft thereof extending through vertical openings in the rotating frame. These existing designs incorporate a long main rotating shaft which connects the gear case mounted on the top deck of the rotating frame to the main rotating pinion located below the bottom plate of the rotating frame. The long main rotating shaft is subject to torsional windup which can cause unbalanced motor load sharing. Severe vibrational problems can also occur in this condition. The overhung main rotating pinion loads also cause the main rotating shaft to deflect in bending sufficiently that the pinion teeth must be heavily crowned to compensate for this misalignment. Additionally, such mounting arrangements have been found not to be entirely satisfactory in that configurations require precise machining of the rotating frame for mounting the swing unit and assuring proper alignment of the pinion shaft with the ring gear.
The precise machining of the rotatable frame and the alignment of the pinion shaft with the ring gear involves a comparatively high manufacturing cost. It is highly desirable to provide a swing drive unit for an excavator which can be effectively and economically installed in the machine in the field and properly aligned with the ring gear of the machine to provide full bearing contact between the teeth of the meshing gears and which provides maximum efficiency in torque transmission.
A need has thus arisen for a swing drive unit for an excavating machine which minimizes torsional windup and eliminates shaft bending deflection thereby providing improved tooth contact between the pinion and ring gear. A need has further arisen for an improved swing drive unit which is modular in construction for easy removal for servicing in the field.